The decision follows a strategic review of its business and was made in full consultation with its manufacturing partners.
A Thurlow Nunn spokesman says: “The decision was forced by the considerable investment we feel we would have to make to bring the garage up to the standard we demand.”
The spokesman adds that many people who work at the Downham Market dealership have been offered alternative employment at other Thurlow Nunn operations.
Thurlow Nunn will now operate eight Vauxhall, two Saab, one Chevrolet and one Toyota garage throughout Norfolk, Suffolk and Cambridgeshire. Its turnover is in close to £80m. During the last 12 months it acquired Warwick Schubrook, a group of three Vauxhall outlets.
An agricultural equipment business that Thurlow Nunn operates at the Downham Market site is unaffected by the decision.
A Subaru spokesman says it is now a priority for the brand to appoint a dealer in the west Norfolk area to take over the franchise to maintain its presence there.
Mitsubishi says it is in talks with a couple of potential dealer partners in the area.